"The Propagation of Sound" Various Sound PPT Courseware 4

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"The Propagation of Sound" Various Sound PPT Courseware 4

Thinking: How effective is sound propagation in different objects?

Across the sand, water and air, listen to the gentle tapping of a pencil on the table.

Activity steps

1. Prepare three sealable plastic bags, fill them with sand, water and air respectively and seal them.

2. Clean the table, place one of the plastic bags flat on the table, place one ear gently against the bag, and cover the other ear.

3. At arm's length, tap or rub the table with the eraser on your pencil.

4. What kind of plastic bag contains the best sound? Which bag is least likely to make audible noises?

The propagation of sound requires a medium

Experiments show that sound must pass through a certain substance (such as air) to spread. That is, sound propagates through media.

The material that propagates sound is called the medium of sound

The propagation of sound requires a medium, which can be a gas, liquid or solid. Usually we can hear sounds mainly because air can carry sound.

Sound is transmitted in the form of waves through objects. When sound waves encounter an object, it causes the object to vibrate. This is how sound spreads from one place to another through various materials.

Now can you explain?

There are three famous acoustic buildings in the Temple of Heaven. One is the Circular Mound. The emperors of the Ming and Qing Dynasties would go to the Tianxin Stone in the center every year to pray, "Bless the sky, and have a good harvest." Here he heard his prayers sound louder than usual. Much bigger, he thought it was his piety that moved God, right? This is because the echo formed by the sound being reflected by the surrounding stone railings strengthens the original sound.

think:

Many science fiction movies have scenes of war in space. Do you think you can hear explosions in space?

Answer: You cannot hear the sound of explosions in space because there is no air in space and sound cannot propagate in a vacuum.

think about it

1. We often see scenes like this on TV, where people put their ears on the railway tracks to listen for the sound of trains in the distance. What is going on? (Sound travels at 340 meters per second in air and 5,000 meters per second in solids.)

2. In ancient times, cavalrymen would lie on their sides on the ground when sleeping. Why was this?

3. Why do we always see lightning first and then hear thunder?

4. Can we speak loudly when we are fishing? Why?

How to make a small toy "earth phone"

1. Find two paper cups and poke a small hole in the bottom of each cup.

2. Find a piece of cotton thread, pass it through the holes in the bottom of the two cups, and tie a small toothpick or tie a knot at the end of the thread.

3. Two classmates straightened the cotton thread and spoke softly.

How does sound get from one end of the "earth phone" to the other?

Sound spreads in the form of waves. When sound waves encounter an object, it causes the object to vibrate. This is how sound spreads from one place to another through various materials.

Operation

1. The propagation of sound requires ( ), the medium can be gas, liquid or solid.

2. Propagation speed: solid ( ) liquid ( ) gas

3. Sound is transmitted in the form of waves through objects, and sound propagates toward ( ).

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Update Time: 2024-07-01

This template belongs to science courseware People's Education Press Fourth Grade Science Volume 2 industry PPT template

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